1. Field of the Invention
The present invention relates to a structure of a display panel, and more particularly to a structure of a liquid-crystal-on-silicon (LCoS) panel.
2. Description of the Related Art
Residual direct current (DC) charges are a problem to be solved in liquid crystal displaying devices, wherein the residual DC charge results from the accumulation of ions on pixels of the liquid crystal displaying devices. For example, in the conventional twisted-nematic-type liquid crystal display (LCD) devices, DC charges are accumulated in the interface of the alignment layer of each pixel. The resultant residual DC voltage causes liquid crystal disposed across the region between the pixels and the transparent electrodes to result in the after-image phenomenon. Methods for solving this problem such as using a low-resistance alignment layer have been disclosed, for example, in Japanese Patent Application Laid-Open No. 8-54631.
For liquid-crystal-on-silicon (LCoS) displaying devices, the problem of DC charges may become more serious than that of the twisted-nematic-type LCD devices. The ions are easily accumulated on the pixels due to the different work functions of the different kinds of electrode, e.g., indium tin oxide (ITO) transparent electrode and aluminum (Al) reflective electrode. In particular, when pixelized color filters (i.e. patterning color filters on the chip) are performed in the LCoS panel, DC charges may be non-uniformly distributed on the built-in color filters (CFs) so as to lead to the non-uniformity of an internal electric field and thus cause the liquid crystal molecules to be incompletely rotated. The situation leads to defects such as mura.
FIG. 1 shows a part of structure of a conventional LCoS panel 10. The LCoS panel 10 includes a silicon (Si) substrate 12, a glass substrate 14, a liquid crystal layer 16 and a plurality of CFs 18, wherein DC charges may be distributed non-uniformly on the CFs 18 due to the accumulation of ions. As shown in FIG. 1, the CFs 18 are respectively disposed over a plurality of sub-pixels 20 which are corresponding to the CFs 18 respectively and disposed over the Si substrate 12. Each sub-pixel 20 includes a metal interconnection layer 22, a reflective mirror 24, a protective layer 26 and an anti-reflective layer 28, wherein the metal interconnection layer 22, the reflective mirror 24, the protective layer 26 and the anti-reflective layer 28 and the corresponding CF 18 are disposed on the Si substrate 12 in sequence. FIG. 1 also shows that an insulating layer 30 is disposed on the CFs 18; a plurality of spacing layers 32 are formed between the adjacent sub-pixels 20 and between the adjacent CFs 18; an alignment layer 34 is disposed between the liquid crystal layer 16 and the insulating layer 30; and a plurality of transparent electrodes 36 (only one transparent electrode is viewed in this cross-section shown in FIG. 1) are disposed between the glass substrate 14 and the liquid crystal layer 16.
Nowadays, the LCoS technology integrates an LCD technology with single-crystal Si-based very-large-scale-integration (VLSI) circuits. Compared with the LCD device manufactured by a thin-film transistor (TFT) technology, the LCoS displaying devices is cost-effective. Accordingly, it is worthy to have an innovation on the reduction of the residual DC charges on the CFs in the LCoS displaying devices.